When use is made of a semiconductor chip with circuit elements formed thereon for large scale integration, etc., it is necessary to connect these circuit elements to external circuits. Electrodes are therefore provided on the chip and lead wires for making connections to external circuits are bonded to these electrodes. FIGS. 1A, 1B, 1C and 1D show a cross-sectional schematic view of a section to the semiconductor substrate showing steps in the manufacturing process of the conventional invention.
The process includes first providing a semiconductor substrate 10 such as silicon which includes a plurality of circuit elements and an insulative layer 11 such as SiO.sub.2 formed on the surface of the substrate. An electrode section 12 such as aluminum is then formed on the insulative layer and the electrode section is electrically connected to the circuit elements. A passivation layer 13 is then formed on the insulative layer 11 on an edge portion of the electrode section 12. The center region on the surface of the electrode section 12 is exposed to form a concave portion (FIG. 1A). A first photoresist layer 14 is then formed on the passivation layer 13. A multi-layer film 15 is then formed on the whole surface in a manner so as to cover the exposed electrode section 12. The multi-layer film includes at least two layers such as gold-titanium tungsten (FIG. 1B). A second photoresist layer 16 with a predetermined thickness necessary for forming a bump electrode on the multi-layer film 15 is formed on the multi-layer film 15 over the electrode section 12 and the passivation layer 13 and the first photoresist layer 14. The edge of the second photoresist layer 16 is inside the concave portion of the electrode section 12, and is outside the edge of the multi-layer film 15 over the first photoresist layer 14. A bump electrode 17 of gold crystal is formed on the multi-layer film 15 over the electrode section 12 by electroplating in a manner such that the surface of the bump electrode 17 is controlled to be lower than or equal to the surface of the second photoresist layer 16 (FIG. 1C). The thickness of the photoresist 16 is desired to be the same thickness as the thickness of the bump electrode formed in the later process, but since it is difficult to make the thickness of the bump electrode exactly equal to the surface of the photoresist 16, the thickness of the bump electrode is made actually lower than the thickness of the photoresist 16 in about 2 .mu.m as shown in FIG. 1C. The semiconductor substrate on which the photoresist pattern is formed are dipped in isopropyl alcohol and removed from the device by applying ultrasonic waves, and the multi-layer film 15 above and both sides of the passivation layer 13 are removed by ultrasonic waves in isopropyl alcohol (FIG. 1D). The bump electrode is then subjected to a heat treatment in an inactive atmosphere.
This process for manufacturing the conventional semiconductor device with a bump-electrode of gold crystal has the following drawbacks.
(1) It needs two photo-process and is very complex.
(2) The unnecessary multi-layer metal film cannot always be removed completely (especially when the thickness of the film is 1 .mu.m or more).
(3) Sputtering cannot be used to form a multilayer metal film so that vapor deposition must be used. (If a multi-layer metal film is formed by sputtering, the temperature of the wafer is raised up to about 300.degree. C. so that the photoresist layer will be ashed.)